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 with mineral acids, M2CO8 + 2HCl = 2MCl + H2O + CO2. It is also formed in ordinary fermentation processes, in the combustion of all carbon compounds (oil, gas, candles, coal, &c.), and in the process of respiration.

It is a colourless gas, possessing a faint pungent smell and a slightly acid taste. It does not burn, and does not support ordinary combustion, but the alkali metals and magnesium, if strongly heated, will continue to burn in the gas with formation of oxides and liberation of carbon. Its specific gravity is 1.529 (air = 1). It is readily condensed, passing into the liquid condition at 0° C. under a pressure of 35 atmospheres. Its critical temperature is 31.35° C., and its critical pressure is 72.9 atmos. The liquid boils at &minus;78.2° C. (l atmo.), and by rapid evaporation can be made to solidify to a snow-white solid which melts at &minus;65° C.(see ). Carbon dioxide is moderately soluble in water, its coefficient of solubility at 0° C. being 1.7977 (R. Bunsen). It is still more soluble in alcohol. The solution of the gas in water shows a faintly acid reaction and is supposed to contain carbonic acid, H2CO3. The gas is rapidly absorbed by solutions of the caustic alkalis, with the production of alkaline (q.v.), and it combines readily with potassium hydride to form potassium formate. It unites directly with ammonia gas to form ammonium carbamate, NH2COONH4. It may be readily recognized by the white precipitate which it forms when passed through lime or baryta water. Carbon dioxide dissociates, when strongly heated, into carbon monoxide and oxygen, the reaction being a balanced action; the extent of dissociation for varying temperatures and pressures has been calculated by H. Le Chateller (Zeit. Phys. Chem., 1888, 2, p. 782; see H. Sainte-Claire Deville, Comptes rendus, 1863, 56, p. 195 et seq.). The volume composition of carbon dioxide is determined by burning carbon in oxygen, when it is found that the volume of carbon dioxide formed is the same as that of the oxygen required for its production, hence carbon dioxide contains its own volume of oxygen. Carbon dioxide finds industrial application in the preparation of soda by the Solvay process, in the sugar industry, in the manufacture of mineral waters, and in the artificial production of ice.

Carbonyl chloride (phosgene), COCl2, was first obtained by John Davy (Phil. Trans., 1812, 40, p. 220). It may be prepared by the direct union of carbon monoxide and chlorine in sunlight (Th. Wilm and G. Wischin, Ann., 1868, 14, p. 150); by the action of phosphorus pentoxide on carbon tetrachloride at 200–210° C. (G. Gustavson, Ber., 1872, 5, p. 30), 4CCl4 + P4O10 = 2CO2 + 4POCl3 + 2COCl2; by the oxidation of chloroform with chromic acid mixture (A. Emmerling and B. Lengyel, Ber., 1869, 2, p. 54), 4CHCl3 + 3O2 = 4COCl2 + 2H2O + 2Cl2; or most conveniently by heating carbon tetrachloride with fuming sulphuric acid (H. Erdmann, Ber., 1893, 26, p. 1993), 2SO3 + CCl4 = S2O5Cl2 + COCl2.

It is a colourless gas, possessing an unpleasant pungent smell. Its vapour density is 3.46 (air = 1). It may be condensed to a liquid, which boils at 8° C. It is readily soluble in benzene, glacial acetic acid, and in many hydrocarbons. Water decomposes it violently, with formation of carbon dioxide and hydrochloric acid. It reacts with alcohol to form chlorcarbonic ester and ultimately diethyl carbonate (see ), and with ammonia it yields (q.v.). It is employed commercially in the production of colouring matters (see ), and for various synthetic processes.

Carbon oxysulphide, COS, was first prepared by C. Than in 1867 (Ann. Suppl., 5, p. 236) by passing carbon monoxide and sulphur vapour through a tube at a moderate heat. It is also formed by the action of sulphuretted hydrogen on the isocyanic esters, 2CONC2H5 + H2S = COS + CO(NHC2H5)2, by the action of concentrated sulphuric acid on the isothiocyanic esters, RNCS + H2O = COS + RNH2, or of dilute sulphuric acid on the thiocyanates. In the latter reaction various other compounds, such as carbon dioxide, carbon bisulphide and hydrocyanic acid, are produced. They are removed by passing the vapours in succession through concentrated solutions of the caustic alkalis, concentrated sulphuric acid, and triethyl phosphine; the residual gas is then purified by liquefaction (W. Hempel, Zeit. angew. Chemie, 1901, 14, p. 865). It is also formed when sulphur trioxide reacts with carbon bisulphide at 100° C., CS2 + 3SO3 = COS + 4SO2, and by the decomposition of ethyl potassium thiocarbonate with hydrochloric acid, CO(OC2H5)SK + HCl = COS + KCl + C2H5OH. It is a colourless, odourless gas, which burns with a blue flame and is decomposed by heat. Its vapour density is 2.1046 (air = 1). The liquefied gas boils at &minus;47° C. under atmospheric pressure. It is soluble in water; the aqueous solution gradually decomposes on standing, forming carbon dioxide and sulphuretted hydrogen. It is easily soluble in solutions of the caustic alkalis, provided they are not too concentrated, forming solutions of alkaline carbonates and sulphides, COS + 4KHO = K2CO3 + K2S + 2H2O.

 CARBONADO, a name given in Brazil to a dark massive form of impure diamond, known also as “carbonate” and in trade simply as carbon. It is sometimes called black diamond. Generally it is found in small masses of irregular polyhedral form, black, brown or dark-grey in colour, with a dull resinoid lustre; and breaking with a granular fracture, paler in colour, and in some cases much resembling that of fine-grained steel. Being slightly cellular, its specific gravity is rather less than that of crystallized diamond. It is found almost exclusively in the state of Bahia in Brazil, where it occurs in the cascalho or diamond-bearing gravel. Borneo also yields it in small quantity. Formerly of little or no value, it came into use on the introduction of Leschot’s diamond-drills, and is now extremely valuable for mounting in the steel crowns used for diamond-boring. Having no cleavage, the carbon is less liable to fracture on the rotation of the drill than is crystallized diamond. The largest piece of carbonado ever recorded was found in Bahia in 1895, and weighed 3150 carats. Pieces of large size are, however, relatively less valuable than those of moderate dimensions, since they require the expenditure of much labour in reducing them to fragments of a suitable size for mounting in the drill-heads. Ilmenite has sometimes been mistaken in the South African mines for carbonado.

 CARBONARI (an Italian word meaning “charcoal-burners”), the name of certain secret societies of a revolutionary tendency which played an active part in the history of Italy and France early in the 19th century. Societies of a similar nature had existed in other countries and epochs, but the stories of the derivation of the Carbonari from mysterious brotherhoods of the middle ages are purely fantastic. The Carbonari were probably an offshoot of the Freemasons, from whom they differed in important particulars, and first began to assume importance in southern Italy during the Napoleonic wars. In the reign (1808–1815) of Joachim Murat a number of secret societies arose in various parts of the country with the object of freeing it from foreign rule and obtaining constitutional liberties; they were ready to support the Neapolitan Bourbons or Murat, if either had fulfilled these aspirations. Their watch-words were freedom and independence, but they were not agreed as to any particular form of government to be afterwards established. Murat’s minister of police was a certain Malghella (a Genoese), who favoured the Carbonari movement, and was indeed the instigator of all that was Italian in the king’s policy. Murat himself had at first protected the sectarians, especially when he was quarrelling with Napoleon, but later, Lord William Bentinck entered into negotiations with them from Sicily, where he represented Great Britain, through their leader Vincenzo Federici (known as Capobianco), holding out promises of a constitution for Naples similar to that which had been established in Sicily under British auspices in 1812. Some Carbonarist disorders having broken out in Calabria, Murat sent General Manhès against the rebels; the movement was ruthlessly quelled and Capobianco hanged in September 1813 (see Greco, Intorno al tentativo dei Carbonari di Citeriore Calabria nel 1813). But Malghella continued secretly to protect the Carbonari and even to organize them, so that on the return of the Bourbons in 1815 King Ferdinand IV. found his kingdom swarming with them. The society comprised nobles, officers of the army, small landlords, government officials, peasants and even priests. Its organization was both curious and mysterious, and had a fantastic ritual full of symbols taken from the Christian religion, as well as from the trade of charcoal-burning, which was extensively practised in the mountains of the Abruzzi and Calabria. A lodge was called a vendita (sale), members saluted each other as buoni cugini (good cousins), God was the “Grand Master of the Universe,” Christ the “Honorary Grand Master,” also known as “the Lamb,” and every Carbonaro was pledged to deliver the Lamb from the Wolf, i.e. tyranny. Its red, blue and black flag was the standard of revolution in Italy until substituted by the red, white and green in 1831.

When King Ferdinand felt himself securely re-established at Naples he determined to exterminate the Carbonari, and to this end his minister of police, the prince of Canosa, set up another secret society called the Calderai del Contrappeso (braziers of the counterpoise), recruited from the brigands and the dregs of the people, who committed hideous excesses against supposed Liberals, but failed to exterminate the movement. On the